System for measuring the height above ground level of vehicles

ABSTRACT

A system for measuring a vehicle&#39;s height above ground level including a sensor which is preassembled and incorporated in the shock absorber of the vehicle eliminating assembly operations and fasteners in attaching the unit to the vehicle and protecting the sensor from impacts and the action of external agents due to its shielded position within the shock absorber.

BACKGROUND OF THE INVENTION

The present invention relates to a system for measuring a vehicle'sheight above ground level. More particularly, the system represents aconsiderable technical improvement as compared to such systems presentlyin use, both in regard to reliability and simplicity and consequent costeffectivenss in manufacture and assembly.

When the height above ground level of a vehicle must be known,measurement systems presently employed typically include a sensorlocated between the body (suspended mass) and the wheels (nonsuspendedmass) of the vehicle.

The sensor is physically housed in a container which can be any of manydifferent shapes for being fitted between the body and a part connectedto the wheels, such as an axle, trailing arm, stab axle, etc.

One or more body areas suitable for fitting the sensor must be selected,and one or more fasteners for securing the movable part of the sensor tothe nonsuspended parts of the vehicle and for attaching the in-lineassembly of the sensor must be provided.

The system to which the present invention relates eliminates theserequirements since it employs at least one sensor that is preassembledand incorporated within the shock absorber of the vehicle. Fitting thesensor inside the shock absorber assures its physical protection anddoes away with the mounting operations and fasteners required for thesensors presently available on the market.

The system sensor may be any of the presently known and available types.Four sensor types contemplated for use in the invention are:

A potentiometric contact version, a version involving at least oneHall-effect sensor, a version involving an eddy current detector, and aversion with an ultrasonic distance detector. Other sensors can bedevised and the invention is not to be considered limited to thesesensors.

SUMMARY OF THE INVENTION

The present invention overcomes the shortcomings of the prior art byproviding a position sensor incorporated into the shock absorber of thevehicle for sensing the position of the piston rod of the shock absorberrelative to the bottom of the shock absorber.

According to a preferred embodiment of the invention, a resistance filmis deposited on an inside wall of a working cylinder of the shockabsorber and is contacted by an elctrical slide contact on the piston ofthe shock absorber.

According to another embodiment of the invention, a Hall-effecttransducer is employed including a magnet on the shock absorber pistonand an end instrument on the working cylinder.

Another embodiment of the invention provides for a coil having primaryand secondary windings to be affixed to the working cylinder fordeveloping a magnetic field in one coil and inducing a current in thesecond coil as modulated by the moving piston of the shock absorber.

A still further embodiment of the invention provides for an ultrasonicemitter mounted on the piston of the shock absorber and a reflectingelement on the bottom of the shock absorber. Reflected sound isprocessed for providing an indication of the position of the pistonrelative to the bottom of the shock absorber.

BRIEF DESCRIPTION OF THE DRAWING

The advantages, characteristics, and operation of the system accordingto the present invention will clearly appear from the following DetailedDescription Of The Preferred Embodiment when taken in conjunction withthe drawings of which:

FIG. 1 is a partial, elevation cross-sectional view of a shock absorberemploying a preferred embodiment of the system according the presentinvention incorporating a potentiometric contact version;

FIG. 2 is a partial, cross-sectional elevational view of a shockabsorber showing another embodiment of the system incorporating aHall-effect sensor;

FIG. 3 is a partial, cross-sectional elevational view of a shockabsorber mounting showing a third embodiment of the system incorporatingan eddy current detector;

FIG. 4 is a partial, cross-sectional elevational view of a shockabsorber mounting showing a fourth embodiment of the systemincorporating an ultrasonic distance detector;

FIG. 5 is a partial, cross-sectional elevational view of a shockabsorber showing details of construction of another embodiment of thesystem incorporating a Hall-effect sensor;

FIG. 6 is a partial, cross-sectional view of a shock absorber showingdetails of construction of a still further embodiment of the systemincorporating a Hall-effect sensor; and

FIG. 7 is another embodiment of the system also incorporating aHall-effect sensor showing details of construction.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring to the different figures in the drawings, it is to beunderstood that they show, merely as an example, a Mac Pherson strut,but this in no way shall restrict the application of the systemaccording to the present invention to this particular type of shockabsorber. Identical reference numbers indicate identical or equivalentparts of the system versions illustrated herein.

FIG. 1 shows an embodiment incorporating a potentiometrical contact.

A resistance film 2, across which a voltage V is applied, is depositedon an inside wall of a work cylinder 1 mounted within the container 1which is closed at its lower end by a closure member 11 of a shockabsorber. A pick-up slide 3 secured either to a piston rod 4 or to apiston 5 of the shock absorber slides along the resistance film 2 andpicks up a voltage signal V', which changes with the axial position ofthe piston 5 within the working cylinder 1, so that a direct reading ofits height from the ground may be displayed on a suitably calibratedscale located, for instance, on the instrument panel of the vehicle.

FIG. 2 shows an embodiment incorporating a sensor operating on theprinciple of the well-known Hall effect incorporating a permanentmagnet.

A ring-shaped magnet 7 is secured to the piston rod 4 of the shockabsorber and a Hall-effect sensor 6 is fixed to the outer face ofcylinder 1 which, in this case, is made of a nonmagnetic material. Thesensor 6 supplies a voltage signal, V, modulated according to the axialdistance between the magnet and the sensor. It is also possible to usemore than one magnet and/or more than one sensor and to invert theirmutual position.

FIG. 3 shows an embodiment incorporating an eddy current detector. Acylindrical coil 10 having a primary winding and a secondary windingincorporated into an insulating material is coupled to avoltage/frequency, V,f generator and is affixed onto the outer surfaceof the cylinder 1. When the magnetic flux, which is present within thecoil, is interrupted by a conductive material such as, for example, thepiston 5 moving within the cylinder 1, a decrease in the strength of thehigh-frequency signal across the coil will take place by the action ofthe induced currents.

By considering the assembly as a transformer, the effects due to theenergy dissipated by the secondary winding are carried out to theprimary winding by introducing an equivalent impedance.

By operating over limited distances and with a suitable calibrationrange, it is possible to obtain a linear relationship between the outputvoltage of the coil and the axial position of the piston 5 within thecoil 10.

Other embodiments incorporating the eddy current-type sensor system arealso possible. For example, the primary and secondary windings of thecoil 10 can be separated and arranged in a different manner, such as,for instance, field coils can be affixed to the cylinder 1 and inducedcoils can be keyed onto the piston rod 4. In any case, the systemmeasures the position of the piston and, therefore, the body of thevehicle relative to the bottom of the shock absorber.

FIG. 4 shows the embodiment incorporating an ultrasonic distancedetector. On the piston rod 4 under the piston 5 there is fitted anultrasonic quartz emitter 8 which sends a reference signal to anacoustically reflecting plate 9. A reflected signal returns to thequartz emitter 8 which also acts as an end instrument and which iscoupled to an electronic device which receives, recognizes, demodulates,and converts the incoming signal into a voltage which is proportional tothe distance covered by the ultrasonic wave in reaching the reflectingplate 9.

In all of the above mentioned embodiments, that is, according to FIGS.1, 2, 3 and 4 a continuous output signal from the particular sensorvaries between two values indicating the two extreme position of thewheels with respect to the body.

Moreover, in the embodiment involving the Hall-effect sensor, it is notnecessary that the sensor exciter consists of a permanent magnet but itmay be replaced by any means made of suitable magnetic material, as itis evident from the further versions of this embodiment, illustrated inFIGS. 5 to 7.

FIG. 5 shows a first variation of the embodiment involving Hall-effectsensor. On the outer surface of the cylinder 1, which in this case ismade of nonmagnetic material (e.g. aluminum alloy, stainless steel andso forth), there are fixed two Hall-effect sensors 7 capable to providea voltage signal when faced by a magnetized piston 5 or any othermagnetized material such as 13. When the magnetized piston 5 or the ring13 passes by the sensors 7, signals forming a position reading code ofthe piston 5 are released.

FIG. 6 shows a second variation of the embodiment involving theHall-effect sensors. Two spark plug formed supports 7' each supporting aHall-effect sensor 7 are fixed to the shock absorber housing 1'; thesensing surface of said sensor is facing the nonmagnetic materialcylinder 1. The operation is the same as that described in relation tothe embodiment of FIG. 5. When the piston 5 or the ring 13 passes by thesensors 7, signals defining a position of the piston 5 are obtained.

In this case, it is sufficient to drill two holes in the shockabsorber's outer case 1' to mount the sensors with the evident greatestease in using the system.

FIG. 7 shows a third variation of the embodiment involving theHall-effect sensors. The sensors 7 can be wall mounted, either insidethe shock absorber housing 1' on the outer surface of cylinder 1, asshown in FIG. 5, or screwed into the shock absorber housing 1 as shownin FIG. 6. Both sensors 7 sense the eventual presence of the pistonrod/piston (4,5) assembly in front of them and not just the passage ofthe piston 5 or the ring 13 as in the other variations of theembodiment. The voltage signals obtained from sensors 7 define aposition of the piston 5. A further system variation, also shown in FIG.7, includes fixing to the piston rod 4 a cylindrical pierced cage 12made of magnetic material which permits the passage of the oil duringthe operation of the shock absorber and provides the magnetic materialmass capable of exciting the sensors 7. Such solution can be used whenthe piston rod is too far from sensors 7.

It can be seen that the system, according to the present invention,solves in a simple manner the problem of fitting the sensors inside theshock absorber and offers a wide range of solutions and advantages overpresent techniques.

The inside construction of the shock absorber provides for placement ofthe sensor in an area protected against accidental impacts andenvironmental conditions.

The main advantage of the present invention is found in the fact thatnothing must be added to the vehicle to accommodate the system, nofastening areas must be provided and no assembly and adjustment time isrequired.

It must also be stressed that numerous variations, changes, additionsand/or modifications may be made and those changes, additions, andmodifications are to be considered to be within the scope of theappended claims.

What is claimed is:
 1. An integral hydraulic shock absorber and vehicleheight above ground level sensor for use in a vehicle leveling systemcomprising:an elongated tubular outer casing closed on one end adaptedto be affixed to an unsprung portion of a vehicle; an elongated tubularinner member closed on one end mounted coaxially within said outercasing defining a working chamber at least partially filled with ahydraulic fluid and including a thin film of electrically resistivematerial deposited on an inner surface of said inner tubular member insaid working chamber; said outer casing and said inner member havingcoaxially aligned openings at an end opposite said closed ends, saidinner member sealingly affixed to said outer casing at said endincluding said aligned openings; a piston rod extending axially slidablysealingly through said aligned openings into said working chamber, afree end of said piston rod adapted to be affixed to a sprung portion ofsaid vehicle; a shock absorber piston on said piston rod is said workingchamber; a first electrical connection to said electrically resistivefilm; a second electrical connection to said electrically resistivefilm; a slide contact on said piston in sliding electrical contact withsaid electrically resistive film between said first and said secondelectrical connections; and said first electrical connection, saidsecond electrical connection and said slide contact adapted to becoupled to a circuit of said leveling system to measure voltage changeacross a one of said first or second electrical connections and saidslide contact.
 2. The integral shock absorber and vehicle height aboveground level sensor as defined in claim 1 wherein said first and saidsecond electrical connections to said electrically resistive film arepositioned at predetermined axially spaced apart positions.
 3. Anintegral shock absorber and vehicle height above ground level sensorcomprising:a tubular outer casing closed on one end including means formounting said casing to an unsprung portion of a vehicle; a tubularinner casing closed in one end mounted concentrically within said outercasing and defining a hydraulic shock absorber working chamber, an innersurface of said inner casing including a thin film of electricallyresistive material deposited thereon, a pair of electrical leadselectrically coupled to said film at axially spaced apart locations, apiston rod including a shock absorber piston axially slidably mounted insaid working chamber, said piston rod adapted to be mounted to a sprungportion of the vehicle and an electrical slide contact in contact withsaid film between said spaced apart locations and being moveable oversaid thin film with said piston.